An updated assessment of spp. that associate with common scleractinian corals from Moorea (French Polynesia) reveals high diversity among background symbionts and a novel finding of clade B.

The adaptative bleaching hypothesis (ABH) states that, depending on the symbiotic flexibility of coral hosts (i.e., the ability of corals to "switch" or "shuffle" their algal symbionts), coral bleaching can lead to a change in the composition of their associated community and, thus, contribute to the coral's overall survival. In order to determine the flexibility of corals, molecular tools are required to provide accurate species delineations and to detect low levels of coral-associated . Here, we used highly sensitive quantitative (real-time) PCR (qPCR) technology to analyse five common coral species from Moorea (French Polynesia), previously screened using only traditional molecular methods, to assess the presence of low-abundance (background) spp. Similar to other studies, each coral species exhibited a strong specificity to a particular clade, irrespective of the environment. In addition, however, each of the five species harboured at least one additional clade, among clades A-D, at background levels. Unexpectedly, and for the first time in French Polynesia, clade B was detected as a coral symbiont. These results increase the number of known coral- associations from corals found in French Polynesia, and likely indicate an underestimation of the ability of the corals in this region to associate with and/or "shuffle" different clades. Altogether our data suggest that corals from French Polynesia may favor a trade-off between optimizing symbioses with a specific clade(s), maintaining associations with particular background clades that may play a role in the ability of corals to respond to environmental change.